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Over recent decades, regions of West and Central Africa have experienced different and significant changes in climatic patterns, which have significantly impacted hydrological regimes. Such impacts, however, are not fully understood at the regional scale, largely because of scarce hydroclimatic data. Therefore, the aim of this study is to (a) assemble a new, robust, reconstructed streamflow dataset of 152 gauging stations; (b) quantify changes in streamflow over 1950–2005 period, using these newly reconstructed datasets; (c) significantly reveal trends and variability in streamflow over West and Central Africa based on new reconstructions; and (d) assess the robustness of this dataset by comparing the results with those identified in key climatic drivers (e.g. precipitation and temperature) over the region. Gap filling methods applied to monthly time series (1950–2005) yielded robust results (median Kling-Gupta Efficiency >0.75). The study underlines a good agreement between precipitation and streamflow trends and reveals contrasts between western Africa (negative trends) and Central Africa (positive trends) in the 1950s and 1960s. Homogenous dry conditions of the 1970s and 1980s, characterized by reduced significant negative trends resulting from quasi-decadal modulations of the trend, are replaced by wetter conditions in the recent period (1993–2005). The effect of this rainfall recovery (which extends to West and Central Africa) on increased river flows are further amplified by land use change in some Sahelian basins. This is partially offset, however, by higher potential evapotranspiration rates over parts of Niger and Nigeria. Crucially, the new reconstructed streamflow datasets presented here will be available for both the scientific community and water resource managers.

The main states of the Angola Low (AL) are identified using clustering analysis applied to daily anomalous patterns of 700-hPa wind vorticity over Angola and adjacent countries from November to March for the 1980/81–2014/15 period. At the daily timescale, we examine the extent to which the main states of the AL modulate daily rainfall over southern Africa. At the interannual timescale, we assess both the relationship between the occurrence of these AL states and El Niño southern oscillation (ENSO) and the role of the AL in explaining ENSO’s failure in driving southern African rainfall at times. Three reanalyses are considered to account for uncertainties induced by the scarcity of data available for assimilation over southern Africa. Three preferential states of the Angola Low are identified: AL state close to its seasonal climatology with slight zonal displacements, anomalously weak AL state and anomalously strong AL state with meridional displacements. These different states all significantly modulate daily southern African rainfall. Near-climatological AL state promotes wet rainfall anomalies over eastern subtropical southern Africa and dry rainfall anomalies over its western part. A slight westward shift in the near-climatological position of the AL leads to reversed zonal gradient in rainfall. The remaining regimes significantly modulate the meridional gradient in southern African rainfall. Anomalously weak and anomalously northward AL states promote wet rainfall anomalies over tropical southern Africa and dry rainfall anomalies over subtropical southern Africa. The reverse prevails for anomalously southward AL. At the interannual timescale, ENSO significantly modulates the seasonal occurrence of most AL states in the three reanalyses. Anomalously weak and southward AL states are more strongly correlated with regional rainfall than ENSO in all reanalyses, suggesting that accounting for AL variability may improve seasonal forecasts. Case study analysis of the major 1982/83 and 1997/98 El Niño events suggests that the weak rainfall anomalies and strong seasonal AL in 1997/98 may result from counteracting effects between ENSO and Indian Ocean coupled modes of variability.

23 pages; International audience; This study provides the first assessment of CMIP5 model performances in simulating southern Africa (SA) rainfall variability in austral summer (Nov–Feb), and its teleconnections with large-scale climate variability at different timescales. Observed SA rainfall varies at three major timescales: interannual (2–8 years), quasi-decadal (8–13 years; QDV) and interdecadal (15–28 years; IDV). These rainfall fluctuations are, respectively, associated with El Niño Southern Oscillation (ENSO), the Interdecadal Pacific Oscillation (IPO) and the Pacific Decadal Oscillation (PDO), interacting with climate anomalies in the South Atlantic and South Indian Ocean. CMIP5 models produce their own variability, but perform better in simulating interannual rainfall variability, while QDV and IDV are largely underestimated. These limitations can be partly explained by spatial shifts in core regions of SA rainfall variability in the models. Most models reproduce the impact of La Niña on rainfall at the interannual scale in SA, in spite of limitations in the representation of ENSO. Realistic links between negative IPO are found in some models at the QDV scale, but very poor performances are found at the IDV scale. Strong limitations, i.e. loss or reversal of these teleconnections, are also noted in some simulations. Such model errors, however, do not systematically impact the skill of simulated rainfall variability. This is because biased SST variability in the South Atlantic and South Indian Oceans strongly impact model skills by modulating the impact of Pacific modes of variability. Using probabilistic multi-scale clustering, model uncertainties in SST variability are primarily driven by differences from one model to another, or comparable models (sharing similar physics), at the global scale. At the regional scale, i.e. SA rainfall variability and associated teleconnections, while differences in model physics remain a large source of uncertainty, the contribution of internal climate variability is increasing. This is particularly true at the QDV and IDV scales, where the individual simulations from the same model tend to differentiate, and the sampling error increase.

International audience; During the austral summer season (November–February), southern African rainfall, south of 20°S, has been shown to vary over a range of time scales, from synoptic variability (3–7 days, mostly tropical temperate troughs) to interannual variability (2–8 years, reflecting the regional effects of El Niño–Southern Oscillation). There is also evidence for variability at quasi-decadal (8–13 years) and interdecadal (15–28 years) time scales, linked to the interdecadal Pacific oscillation and the Pacific decadal oscillation, respectively. This study aims to provide an overview of these ranges of variability and their influence on regional climate and large-scale atmospheric convection and quantify uncertainties associated with each time scale. We do this by applying k-means clustering onto long-term (1901–2011) daily outgoing longwave radiation anomalies derived from the 56 individual members of the Twentieth Century Reanalysis. Eight large-scale convective regimes are identified. Results show that 1) the seasonal occurrence of the regimes significantly varies at the low-frequency time scales mentioned above; 2) these modulations account for a significant fraction of seasonal rainfall variability over the region; 3) significant associations are found between some of the regimes and the aforementioned modes of climate variability; and 4) associated uncertainties in the regime occurrence and convection anomalies strongly decrease with time, especially the phasing of transient variability. The short-lived synoptic anomalies and the low-frequency anomalies are shown to be approximately additive, but even if they combine their respective influence at both scales, the magnitude of short-lived perturbations remains much larger.

Following a request from the European Commission, the EFSA Plant Health Panel updated its pest categorisation of Xylella fastidiosa, previously delivered as part of the pest risk assessment published in 2015. X. fastidiosa is a Gram‐negative bacterium, responsible for various plant diseases, including Pierce's disease, phony peach disease, citrus variegated chlorosis, olive quick decline syndrome, almond leaf scorch and various other leaf scorch diseases. The pathogen is endemic in the Americas and is present in Iran. In the EU, it is reported in southern Apulia in Italy, on the island of Corsica and in the Provence‐Alpes‐Côte d'Azur region in France, as well as in the Autonomous region of Madrid, the province of Alicante and the Balearic Islands in Spain. The reported status is ‘transient, under eradication’, except for the Balearic Islands, Corsica and southern of Apulia, where the status is ‘present with a restricted distribution, under containment’. The pathogen is regulated under Council Directive 2000/29/EC and through emergency measures under http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32015D0789 (as amended http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32017D2352). The pest could enter the EU via host plants for planting and via infectious insect vectors. The host range includes hundreds of host species listed in the EFSA host plant database. In the EU, host plants are widely distributed and climatic conditions are favourable for its establishment. X. fastidiosa can spread by movement of host plants for planting and infectious insect vectors. X. fastidiosa is known to cause severe direct damage to major crops including almonds, citrus, grapevines, olives, stone fruits and also forest trees, landscape and ornamental trees, with high impacts. The criteria assessed by the Panel for consideration as a potential Union quarantine pest are met (the pathogen is present in the EU, but it has a restricted distribution and is under official control). X. fastidiosa is not considered as a regulated non‐quarantine pest (RNQP) as the pathogen may spread also via insect vector transmission.

International audience

13 pages; International audience; El Niño-Southern Oscillation (ENSO) shows a large diversity of events that is modulated by climate variability and change. The representation of this diversity in climate models limits our ability to predict their impact on ecosystems and human livelihood. Here, we use multiple observational datasets to provide a probabilistic description of historical variations in event location and intensity, and to benchmark models, before examining future system trajectories. We find robust decadal variations in event intensities and locations in century-long observational datasets, which are associated with perturbations in equatorial wind-stress and thermocline depth, as well as extra-tropical anomalies in the North and South Pacific. Some climate models are capable of simulating such decadal variability in ENSO diversity, and the associated large-scale patterns. Projections of ENSO diversity in future climate change scenarios strongly depend on the magnitude of decadal variations, and the ability of climate models to reproduce them realistically over the 21 st century.

International audience

In a context of climate, environmental, ecological and socio-economical changes, understanding and predicting the response of hydrological systems on regional to global spatial scales, and on infra-seasonal to multidecadal time-scales, are major topics that must be considered to tackle the challenge of water resource management sustainability. In this context, a number of strongly-linked key issues need to be addressed by the scientific community, including: (i) identifying climate drivers of hydrological variations, (ii) understanding the multi-frequency characteristics of hydroclimate variability, including evolution of extremes (meteorological/hydrological event scale to long-term natural/internal climate- or anthropogenic-driven variations and trends), (iii) assessing the influence of local- to regional-scale basin properties on hydrological system response to climate variability and change, (iv) identifying the evolving contribution of anthropogenic water use in observed hydrological variations. Based on pan-European collaborations, activities of the EURO-FRIEND “Large-scale variations in hydrological characteristics” group aim at generating new findings to improve our understanding of hydrological systems behavior sensu lato (i.e. surface and sub-surface) on large spatial and temporal scales (i.e continental – multidecadal). Through selected examples, this contribution emphasizes recent research developments in characterizing and modeling of climate-hydrology linkages at different temporal and spatial scales, as well as recent insights on climate-hydrology scaling characteristics (i.e. long-term persistence, dependance of processes, of hydrological behaviors, of large-scale climate/hydrology linkages on time-/spatial scales), long-term hydrometeorological reconstructions, and large-scale hydrological model refinement taking into account spatial heterogeneity of watershed physical characteristics.

L’impact du changement climatique sur les ressources en eau est une préoccupation majeure, tant pour les scientifiques que pour les opérationnels. L’état de l’art sur les modifications du cycle de l’eau dans ce contexte d’influence anthropique met en avant deux points : i) l’influence humaine sur la circulation atmosphérique à large échelle, les précipitations, les débits et les niveaux piézométriques est difficile à caractériser car la variabilité naturelle est importante et peut compenser l’impact anthropogénique; ii) bien que dans certains scénarios, les projections CMIP5/6 convergent sur les tendances, elles sous ou sur-estiment les changements sur le cycle de l’eau. Les projections de débits et niveaux de nappes sont affectées par le biais supplémentaire lié au filtre du bassin versant. Les incertitudes liées à la variabilité naturelle, aux biais des modèles, et au filtre du bassin versant sont différentes selon les échelles de temps considérées, impliquant i) que les projections de précipitation, servant d’entrée pour la simulation de débits et niveaux de nappes, sont sous/sur-estimées seulement pour certaines composantes (i.e. oscillations à certaines échelles de temps) ; ii) que la réponse des débits et niveaux de nappe aux projections de précipitation biaisées est modulée par le bassin versant. Dans ce volet de la phase 8, nous étudions la réponse des débits et niveaux piézométriques sur le bassin de la Seine aux précipitations dont certaines composantes ont été modifiées. La méthodologie repose sur la modification spectrale de chroniques de précipitation SAFRAN, en augmentant ou diminuant l’amplitude de certaines composantes par méthodes spectrales, puis en utilisant ces chroniques modifiées en entrée de la plateforme de modélisation CaWaQS afin d’établir une régionalisation de la sensibilité des débits et niveaux piézométriques aux modifications dans les précipitations.

International audience

Understanding how water resources vary in response to climate at different temporal and spatial scales is crucial to inform long-term management. Climate change impacts and induced trends may indeed be substantially modulated by low-frequency (multi-year) variations, whose strength varies in time and space, with large consequences for risk forecasting systems. In this study, we present a spatial classification of precipitation, temperature, and discharge variability in France, based on a fuzzy clustering and wavelet spectra of 152 near-natural watersheds between 1958 and 2008. We also explore phase–phase and phase–amplitude causal interactions between timescales of each homogeneous region. A total of three significant timescales of variability are found in precipitation, temperature, and discharge, i.e., 1, 2–4, and 5–8 years. The magnitude of these timescales of variability is, however, not constant over the different regions. For instance, southern regions are markedly different from other regions, with much lower (5–8 years) variability and much larger (2–4 years) variability. Several temporal changes in precipitation, temperature, and discharge variability are identified during the 1980s and 1990s. Notably, in the southern regions of France, we note a decrease in annual temperature variability in the mid 1990s. Investigating cross-scale interactions, our study reveals causal and bi-directional relationships between higher- and lower-frequency variability, which may feature interactions within the coupled land–ocean–atmosphere systems. Interestingly, however, even though time frequency patterns (occurrence and timing of timescales of variability) were similar between regions, cross-scale interactions are far much complex, differ between regions, and are not systematically transferred from climate (precipitation and temperature) to hydrological variability (discharge). Phase–amplitude interactions are indeed absent in discharge variability, although significant phase–amplitude interactions are found in precipitation and temperature. This suggests that watershed characteristics cancel the negative feedback systems found in precipitation and temperature. This study allows for a multi-timescale representation of hydroclimate variability in France and provides unique insight into the complex nonlinear dynamics of this variability and its predictability.

International audience; The use of several plant protection inputs of mineral origin, such as copper, sulphur or mineral oils is seen as contentious by many consumers and stakeholders within the organic sector. Although the use of these inputs is legal in organic systems and also applied in non-organic agriculture, their use by organic growers raises questions for organic practice, which aspires to be free from toxic, non-renewable chemicals. Data on the current use of permitted plant protection inputs is currently scarce, especially in horticulture where chemical inputs deserve special attention since horticultural products are often readily edible. A mapping of the use of copper, sulphur and mineral oils was conducted by collecting expert knowledge across 10 European countries during May–October 2018, i.e. before the limitation of copper use to 4 kg ha−1 year−1 from February 1, 2019. Results show that copper is widely used by Mediterranean organic growers in citrus, olive, tomato and potato production. The annual limit of 6 kg ha−1 year−1 was not always respected. We also found that tomato producers apply high amounts of copper in winter crops in greenhouses. Mineral oils are applied to control scales, mites and whiteflies. Sulphur is also commonly used by organic vegetable growers, especially in greenhouses. We conclude that the high usage found in various different crops (especially Mediterranean crops) confirms the need for researching alternatives.

National development and resilience are strained by shifting regional water storage patterns. The water shifting pattern has been found over China, but the underlying climate mechanisms of the pattern remain largely unexplored. In this study, how shifting regional moisture conditions are related to intra-annual and inter-annual atmospheric oscillations can be explored by terrestrial water storage (TWS) derived from the Gravity Recovery and Climate Experiment (GRACE). Using a principal component analysis (PCA), the TWSs over the East China were divided into two spatial empirical orthogonal functions (EOFs), accounting for more than 70% of the total spatial variance. The first TWS EOF is related to the seasonal variation, whereas the second TWS EOF is associated with the spatial distribution of TWS trend. In addition, the PCA trend results for precipitation and actual evapotranspiration (ET) are consistent with TWS, with a correlation of 0.44 (p ≪ 0.05) and −0.47 (p ≪ 0.05), respectively. Based on these PCA results, the Yangtze River Basin (YARB) was wetting, while the North China Plain (NCP) was drying between 2003 and 2015. This unbalance water distribution pattern was potentially linked to regional changes of the Hadley-type meridional circulation which aggravated the unevenness between north and south water distributions over the East China. Furthermore, a wavelet transform coherence (WTC) analysis was used for investigating multi-scale relationships between TWS and different climate factors. The local wind intensity and Asian monsoons were related to the regional unbalance TWS pattern on an intra-annual scale, with significance correlations of −0.49 (at p ≪ 0.05) and 0.9 (at p ≪ 0.05) respectively. Meanwhile El Nino Southern Oscillations (ENSO) was significantly negatively linked (correlation of −0.41, p ≪ 0.05) with TWS variability at the inter-annual scale. However, based on partial WTC results, the association between ENSO and TWS can be explained away by the Asian monsoons, so that ENSO is only indirectly related to TWS through monsoons. Overall, the approaches and results of this study not only explained that the shifting TWS distribution over the East China was related to varying strength of local wind intensity and Asian monsoons, and ENSO at intra-annual and inter-annual scales respectively, but also provided a framework for studying TWS redistribution over other regions, which are crucial for sustainable regional development and resilient water future.

Hydrological processes vary over long time-scales, which are originating from large-scale climate. It is not always straightforward, however, to identify how large-scale climate variability can affect regional or local-scale hydrological processes, as such relationships are not linear. Taking the example of the Seine river watershed (northern France), we study the modalities of precipitation and chalk aquifer groundwater level (GWL) variability, focusing on interannual (4-12 years) and interdecadal (12-23 years) scales. We propose a methodological approach for analysing and discussing potential large-scale relationships and forcings on hydrological systems. 163 GWL and 13 precipitation monthly time series, covering the northern half of metropolitan France between 1964 and 2015, were analysed using continuous and discrete multiresolution wavelet transforms. GWL time series all revealed statistically significant oscillating components on interannual and interdecadal scales, but with different amplitudes in space. All precipitation time series displayed the same oscillating components across the watershed with rather constant amplitudes spatially, contrary to GWL time series, which suggest an impact of local physical watershed properties to filter some parts of the climate signal. Using precipitation and GWL time series available over one century, as well as the NOAA 20CR reanalysis, we then analysed the relationship with the North Atlantic atmospheric circulation at both the interannual and interdecadal scales. On interannual scale, using sea-level pressure and geopotential height at 200 hPa, we found that precipitation and GWL variability would be linked to pronounced Rossby wave-like patterns. On interdecadal scale, the patterns obtained correspond to clear west-circulation patterns, which are very similar to the patterns associated with Atlantic Multidecadal Oscillation (AMO). Interdecadal precipitation variability are indeed also found to be consistent with the positive and negative phases of the AMO, suggesting potential impacts on hydrological variability. Examining both precipitation and GWL, major droughts occured during low levels of interannual and interdecadal components. This study therefore demonstrates that such extreme events would then be: i) linked to a weakened western circulation with strong North-South jet stream oscillations on interannual scale; ii) modulated by western circulation associated with the AMO on interdecadal scale.

Climate change is expected to significantly impact on the availability of water resources in West and Central Africa through changes in rainfall, temperature and evapotranspiration. Understanding these changes in this region, where surface water is fundamental for economic activity and ecosystem services, is of paramount importance. In this study, we examine the potential impacts of climate variability and change on hydrological systems by the mid-21st century in West and Central Africa, as well as the uncertainties in the different climate-impact modelling pathways. Simulations from nine global climate models downscaled using the Rossby Centre Regional Climate model (RCA4) are evaluated and subsequently bias-corrected using a nonparametric trend-preserving quantile mapping approach. We then use two conceptual hydrological models (GR2M and IHACRES), and a regression-based model built upon multi-timescale sea surface temperatures and streamflow teleconnections, to understand hydrological processes at the subcontinental scale and provide hydrological predictions for the near-term future (2020-2050) under the RCP4.5 emission scenario. The results highlight a zonal contrast in future precipitation between western (dry) and eastern (wet) Sahel, and a robust signal in rising temperature, suggesting an increase in potential evapotranspiration, across the multi-model ensemble. Overall, across the region, a significant increase in discharge (similar to + 5%) is expected by the mid-21st century, albeit with high uncertainties reported over most of Central Equatorial Africa inherent to climate models and gridded observation data quality. Interestingly, in this region, teleconnections-based regression models tend to be an alternative to hydrological models.

Midlatitude droughts are affected by the tropical disturbances, which are linked to sea-surface temperature patterns in the Pacific and Atlantic Oceans. The combined effects of these two ocean basins manifest themselves in the variation of streamflows, from land surface filtering. In this study, we have developed a framework to explore the effects of global sea surface temperature variations along with atmospheric teleconnection patterns, on local hydroclimatic conditions related to droughts over the Seine catchment, a main waterway in northern France. Using the Standardized Runoff-discharge Index (SRI) to quantify hydrological drought conditions over the Seine, the North Atlantic Oscillation (NAO) index was found to be a significant driver for the upstream dryness between 2001 and 2015. The El Nino Southern Oscillation (ENSO) index was also found to be a significant forcing variable, but for the Seine downstream. The Atlantic Multidecadal Oscillation (AMO) and the West Mediterranean Sea (WMED) indices were significant over almost the whole Seine River basin. Results show that the drought spatial patterns of the Seine River vary differently with the atmospheric and oceanic oscillations from interannual to decadal scales. Over a small catchment with a drainage area around 78,700 square kilometres, the spatial drought variations in the Seine catchment appear to be usual, and they are likely to be related to regional conditions which drive local land surface mechanisms linked with microclimates or geological processes. In general, during the negative phase of AMO and the positive phase of ENSO, the sea surface temperature of the North Atlantic Ocean is low. The positive phase of NAO also lowers sea surface temperatures of the North Atlantic Ocean and the West Mediterranean Sea. Droughts are likely to occur at the Seine during the negative phase of AMO and the positive phase of NAO, because the cold North Atlantic Ocean has less evaporation and provides less moisture to France. Based on these results, a statistical downscaling model is developed to relate SRI to atmospheric and oceanic oscillation indices, which are derived from the Institut Pierre Simon Laplace climate model (IPSL-CM5) outputs. Using this statistical downscaling model and scenarios of Representative Concentration Pathways (RCP4.5 and RCP8.5), the drought conditions of the Seine are projected for the mid- and long-term future (2050s and 2080s). Diverse drought results are obtained. Based on relative importance of oscillation indices, the implications of diverse projections for general drought managements in midlatitude regions related to tropical sea surface temperature disturbances and atmospheric teleconnections are discussed.

20 pages; International audience; We assess the ability of the DePreSys3 prediction system to predict austral summer precipitation (DJF) over southern Africa, defined as the African continent south of 15°S. DePresys3 is a high resolution prediction system (at a horizontal resolution of ~ 60 km in the atmosphere in mid-latitudes and of the quarter degree in the Ocean) and spans the long period 1959–2016. We find skill in predicting interannual precipitation variability, relative to a long-term trend; the anomaly correlation skill score over southern Africa is greater than 0.45 for the first summer (i.e. lead month 2–4), and 0.37 over Mozambique, Zimbabwe and Zambia for the second summer (i.e. lead month 14–16). The skill is related to the successful prediction of the El-Nino Southern Oscillation (ENSO), and the successful simulation of ENSO teleconnections to southern Africa. However, overall skill is sensitive to the inclusion of strong La-Nina events and also appears to change with forecast epoch. For example, the skill in predicting precipitation over Mozambique is significantly larger for the first summer in the 1990–2016 period, compared to the 1959–1985 period. The difference in skill in predicting interannual precipitation variability over southern Africa in different epochs is consistent with a change in the strength of the observed teleconnections of ENSO. After 1990, and consistent with the increased skill, the observed impact of ENSO appears to strengthen over west Mozambique, in association with changes in ENSO related atmospheric convergence anomalies. However, these apparent changes in teleconnections are not captured by the ensemble-mean predictions using DePreSys3. The changes in the ENSO teleconnection are consistent with a warming over the Indian Ocean and modulation of ENSO properties between the different epochs, but may also be associated with unpredictable atmospheric variability.

International audience; Droughts and floods are responsible for ~ 80% of fatalities, and ~70% of economic losses related to natural hazards in Sub-Saharan Africa. Rainfall variability which is driven by interannual to multi-decadal climate fluctuations, here underpins these issues but is also crucial to agriculture and livelihoods. However, due to data scarcity, little is known about the impact of these climatic fluctuations and catchment properties on streamflow variability. Therefore, in this study, using a newly reconstructed streamflow dataset, we aim to extend understanding of hydrological variability through investigation of key large-scale controls which modulate climate-river flows relationships at the subcontinental scale. Modes of variability are extracted using continuous wavelet transform and maximum overlap discrete wavelet transform. We first assess the relative importance of catchment properties in modulating streamflow and modes of variability, before examining teleconnections with climate variables from different datasets (ERSST.v5 and 20CR.v2). The results underline the importance of interannual components of river flow along the Gulf of Guinea and the coastal regions of Central Africa where annual rainfall amounts are higher, and runoff is mostly generated from surface and sub-surface processes. In contrast, river flows along the Sahelian band show stronger multi-decadal components: this partly reflects the prominent role of geological formations in modulating high frequency rainfall signals. These modes of variability (also significantly detected in rainfall) are likely related to anomalies in sea-surface temperature (SST) anomaly patterns and associated atmospheric circulations, which together modulate the West African monsoon. Clarifying the picture of streamflow variability in western and Central Africa thus opens up the prospect for improved future predictions for streamflow and water resources in data scarce environments.

International audience; Climate warming is expected to significantly impact hydrological systems, through changes in rainfall, temperature and evapotranspiration over West and Central Africa. Understanding these changes over this part of the world, where surface water is fundamental for economic activity and ecosystem services, is of paramount importance. In this study, we investigate the main modes of hydroclimatic variability and the potential impacts of climate change on water resource availability by the mid-21st century in West and Central Africa. Climate simulations from the Rossby Centre Regional Climate model (RCA4) driven by 9 Global Climate Models available within the CORDEX initiative are evaluated and bias corrected using a nonparametric trend preserving quantile mapping approach. We then make use of two conceptual hydrological models (GR2M and IHACRES) and a regression-based model built upon multi-scale sea surface temperatures and streamflow teleconnections to understand hydrological processes at the subcontinental scale and provide future hydrological predictions for the near-term (2020-2050) under RCP45 emission scenario. The results highlight a zonal contrast in future precipitation between western (dry) and eastern (wet) Sahel and a clear signal of increasing potential evapotranspiration induced by rising temperatures for all models. Overall mild (±5%) changes in discharge are expected by mid-21st century over the region with however high uncertainties reported over most of Central Equatorial Africa inherent to climate model scenarios and observation datasets quality

publié en ligne le 1er février 2018; International audience; AbstractFew scholars have investigated the economic viability of urban farms in industrialized countries. This study focused on urban community microfarms—small-scale organic market gardens committed to social work activities—in London. Our objective was to investigate the extent to which economic viability was (i) possible for urban microfarms in London and (ii) compatible with the other social and ecological aspirations of microfarmers. The simulation model MERLIN was adapted to London, based on 10 case studies. We analyzed the likelihood of viability—that is, the percentage of economically viable simulations (out of 1000 simulations)—of 192 different strategic scenarios of microfarms. Based on the modeling outputs, a collective workshop was organized with 11 urban farmers to discuss the possibility of reconciling socio-ecological aspirations and economic viability in an urban context. This is the first time that modeling and discussions with stakeholders are combined to explore the viability of urban agriculture. Our novel study shows that urban microfarms can be viable and that viability can be increased by focusing on short-cycle and high added-value leaf vegetables grown in high tunnels and sold at high prices to restaurants. Such strategies can lead urban farmers to make trade-offs with their socio-ecological aspirations. Costs can be decreased by taking advantage of community resources such as volunteer labor or agreements with local councils to rent land at a low rate. Social work (training, hosting community events) is a key condition to access these resources but entails more complex farm management.

Aim To collect and identify the issues that may affect the future global and local management of biological invasions in the next 20 to 50 years and provide guidance for the prioritisation of actions and policies responding to the management challenges of the future. Location Global Methods We used an open online survey to poll specialists and stakeholders from around the world as to their opinion on the three most important future issues both globally and at their respective local working level. Results The 240 respondents identified 629 global issues that we categorised into topics. We summarised the highest rated topics into five broad thematic areas: (1) environmental change, particularly climate change, (2) the spread of species through trade, (3) public awareness, (4) the development of new technologies to enhance management, and (5) the need to strengthen policies. The respondents also identified 596 issues at their respective local working levels. Management, early detection, prevention and funding-related issues all ranked higher than at the global level. Our global audience of practitioners, policy makers and researchers also elicited topics not identified in horizon scanning exercises led by scientists including potential human health impacts, the need for better risk assessments and legislation, the role of human migration and water management. Main conclusions The topic areas identified in this horizon scan provide guidance where future policy priorities for invasive alien species should be set. First, to reduce the magnitude and speed of environmental change and its impacts on biological invasions; second, to restrict the movement of potentially invasive alien species via trade; third, to raise awareness with the general public and empower them to act; and finally, to invest in innovative technologies that can detect and mitigate adverse impacts of introduced species.

Trend and variability in western and central Africa streamflow and its relation to climate variability between 1950 and 2005 3. Trend vs. variability in rainfall and streamflow 4. Teleconnections with global SST anomalies

Horizon scanning for future issues affecting invasive species management: The first phase of the Alien Futures project. Neobiota 2016: 9. International Conference on Biological Invasions Biological Invasions: Interactions with Environmental Change

Colloque avec actes et comité de lecture. Internationale.; International audience

Colloque avec actes et comité de lecture. Internationale.; International audience

Colloque avec actes et comité de lecture. Internationale.; International audience

Colloque avec actes et comité de lecture. Internationale.; International audience

International audience

International audience

25 pages; International audience; This study examines for the first time the changing characteristics of summer and winter southern African rainfall and their teleconnections with large-scale climate through the dominant time scales of variability. As determined by wavelet analysis, the austral summer and winter rainfall indices exhibit three significant time scales of variability over the twentieth century: interdecadal (15–28 years), quasi-decadal (8–13 years), and interannual (2–8 years). Teleconnections with global sea surface temperature and atmospheric circulation anomalies are established here but are different for each time scale. Tropical/subtropical teleconnections emerge as the main driver of austral summer rainfall variability. Thus, shifts in the Walker circulation are linked to the El Niño–Southern Oscillation (ENSO) and, at decadal time scales, to decadal ENSO-like patterns related to the Pacific Decadal Oscillation and the Interdecadal Pacific Oscillation. These global changes in the upper zonal circulation interact with asymmetric ocean-atmospheric conditions between the South Atlantic and South Indian Oceans; together, these lead to a shift in the South Indian Convergence Zone and a modulation of the development of convective rain-bearing systems over southern Africa in summer. Such regional changes, embedded in quasi-annular geopotential patterns, consist of easterly moisture fluxes from the South Indian High, which dominate southerly moisture fluxes from the South Atlantic High. Austral winter rainfall variability is more influenced by midlatitude atmospheric variability, in particular the Southern Annular Mode. The rainfall changes in the southwestern regions of southern Africa are determined by asymmetrical changes in the midlatitude westerlies between the Atlantic and Indian Oceans.